The present invention relates to a wind power generation apparatus using an AC energization synchronous generator connected to a power network, and more particularly to a power generation apparatus having a generator without a rotor position sensor.
In an AC energization synchronous generator for example a doubly-fed generator or a wound-rotor induction generator, used for a wind power generation apparatus, as a rotor winding of a power converter is excited at a slip frequency, a stator side can output an AC voltage having the same frequency as that of a network frequency, a rotation speed can be made variable, and a capacity of the power converter can be reduced.
In a system using an AC energization synchronous generator, a power converter capacity is often smaller than a generator capacity. In such a case, it is necessary to operate the generator synchronously with a network when the generator rotation speed enters a predetermined range. From this reason, a wind power generation apparatus is frequently stopped and operated under the influence of strong and weak wind.
Activation of a wind power generation system using an AC energization synchronous generator starts in a state that a switch connecting a generator stator and a network is open. First, a wind turbine starts rotating by wind. Next, a wind turbine control apparatus instructs a voltage synchronous operation of synchronizing the voltage amplitudes and phases of both the generator stator and the network. At this time, an excitation apparatus excites a rotor winding at a difference frequency (slip frequency) between a network frequency and a rotor frequency calculated by a rotor rotation speed detector. Therefore, the stator can generate a frequency almost coincident with the network frequency at the energization initial stage. When synchronization of the amplitudes and phases of the stator and a network voltage is completed, the switch is closed to electrically connect the generator and network to feed power from the generator to the network.
JP-A-2000-308398 (FIG. 1, description of paragraphs [0027] to [0035]) discloses the operation of synchronizing and the operation of connecting to the network for a variable speed pumped storage power generation apparatus equipped with an AC energization synchronous generator.